Food Allergy Testing for Children

Healthy children with no allergy-related symptoms do not need routine food allergy testing； For children with suspected allergies, a single test result cannot be used as the basis for diagnosis. It must be comprehensively judged based on clinical symptoms and dietary history. Blindly following the test results and eating and drinking randomly may affect the child's growth and development.

Last week, a 3-year-old boy was picked up at the outpatient clinic. His mother came in with a thick test report in hand, her eyes red, and said that the baby had been tested for 20 kinds of food, 12 of which were positive, and even rice and wheat were on the allergy list. For the past six months, the family had been cooking special multigrain rice for the baby. As a result, the baby weighed 2 kilograms less than the standard for his age and was half a head shorter. I flipped through the report and asked a few questions about daily diet, and then I found out that the baby had no reaction at all when eating rice or noodles. He had suffered from unexplained eczema twice before. My mother heard from a friend that allergens should be tested early and avoided, so she went to an institution to do a full set of tests and fasted the baby according to the positive list.

To be honest, I have seen too many examples of this kind. The controversy over children's food allergy testing is really high now, and the views of different schools of diagnosis and treatment are quite different. Currently, there are only two tests recognized as effective by the global pediatric allergy community: skin prick test and serum-specific IgE test. The former drops a small amount of allergen test solution on the skin and makes a small incision, and the results can be obtained in 15 minutes. It is suitable for quickly diagnosing immediate allergies. However, if the child has taken anti-allergy drugs before, or even applied eczema cream with hormones, false negatives may occur. The latter draws venous blood to test IgE antibodies for specific foods. It is not affected by medication and the results are more stable. However, it can only reflect the sensitivity of the immune system to that food and cannot be directly equated to "you will be allergic if you eat it." Moreover, both tests detect IgE-mediated immediate allergies - the kind that causes swollen lips, wheezes, and breathlessness within a few minutes to half an hour after eating. If a child eats a certain food for several days before slowly developing eczema, diarrhea, and constipation, these two tests basically cannot detect delayed allergies.

Another pitfall that everyone is most likely to step on is the "food intolerance IgG test" that has been trumpeted by many institutions. The current mainstream consensus on pediatric allergy is that IgG positivity is essentially immune memory, which can only mean that the child has been exposed to this food, which is a normal immune response and is not a sign of allergy at all. There is no basis for following the IgG positive list of taboos. However, a small number of pediatric gastroenterologists hold different opinions. They believe that for children with chronic diarrhea and recurrent abdominal pain whose cause cannot be found for a long time, the IgG results can be used as a reference for dietary adjustments. For example, if the IgG value of a certain food is particularly high, you can try to avoid it for 2-4 weeks to see if the symptoms are relieved. It is not recommended to cut off long-term fasting across the board.

Having said this, someone must ask, if my baby always gets eczema, is it tested or not? I usually don’t write out a test sheet when I come to the clinic. I first review the food diary for two weeks with the parents: what new foods they ate, whether there were any abnormal reactions after eating them, and whether anyone in the family has a history of severe food allergies or asthma. Only when there is a strong suspicion that a certain food is strongly related to symptoms will we prescribe targeted tests for those foods. We will never prescribe a full set of dozens of screening tests - the more types of tests, the higher the probability of false positives, which will cause parents anxiety for no reason.

The current gold standard for diagnosing food allergy is the oral food challenge test, which means that in a hospital with emergency equipment and medical care present, children are allowed to eat the food they are suspected of allergic to starting from a small dose and gradually increasing the dose to observe the reaction. Do not do this test at home. Two months ago, a 5-year-old baby was admitted to the emergency department. The mother tested positive for peanuts. She wanted to test whether she could tolerate it at home. She gave the baby half a peanut. Within ten minutes, the baby developed laryngeal edema and difficulty breathing. He was intubated and sent to the ICU in the middle of the night. Fortunately, he was rescued in the end.

Of course, some scholars hold different views. They believe that high-risk infants whose parents and siblings have a history of severe food allergy can undergo a simple screening before adding complementary foods at 6 months of age, and only check the IgE of highly allergenic foods such as milk, eggs, and peanuts. If the value is particularly high, it can be added more slowly and gradually under the guidance of a doctor to reduce the risk of severe allergies. However, this view has not yet entered the routine diagnosis and treatment guidelines and can only be used as an optional reference for high-risk families.

In fact, in the final analysis, allergy testing is just an auxiliary tool, and the child's true physical reaction is the most accurate criterion. My relative's baby previously tested positive for egg IgE, and the value was quite high, but she had no problem eating steamed eggs, so I let her eat them normally. Now after eating them for more than half a year, the IgE level has dropped to the normal range during the last review. There is really no need to deprive your child of the joy of eating cakes and drinking milk tea just for a test report, let alone delaying your child's growth and development because of random food taboos. After all, eating well and growing healthy is the top priority in raising a child, right?